1. Field of the Invention
The present invention relates generally to a lens array used in, for instance, a solid-state imaging element or a panel display element. The present invention further relates to a solid-state imaging element and a panel display element, each of which is provided with a lens array.
2. Related Background Art
The following description will depict a typical conventional solid-state imaging element.
FIG. 6 is a cross-sectional view illustrating a schematic configuration of a typical solid-state imaging element.
Generally, a solid-state imaging element includes, as shown in FIG. 6, an n-type semiconductor substrate 312, a p-type well layer 311, light receiving sections 310, charge transfer sections 309, a film 307 made of either silicon oxide or silicon nitride, polysilicon electrodes 308, metal light-shielding layers 306, an element-surface protective layer 305, a flattening film 304, a color filter layer 303, an intermediate transparent film 302, and a lens array (on-chip lens) 301. Incidentally, the color filter layer 303 is unnecessary in the case of a three-plate-type imaging element or a monochrome imaging element, or in the case where incident light has already been subjected to color segmentation by another wavelength selecting means.
In a typical solid-state imaging element, light is received by only the light receiving sections 310, while light incident on the other parts makes no contribution to sensitivity. In view of this, a method has been well known, as one of techniques for providing higher sensitivity, in which a lens array 301 is formed on the light receiving sections 310 to condense beams of light and direct them to the light receiving sections 310.
Lenses of the lens array 301 are disposed at positions corresponding to the light receiving sections 310, respectively, and by utilizing the light collecting effect of each lens, the light entering the same is efficiently guided toward each light receiving section 310.
FIGS. 7A and 7B illustrate a configuration of a conventional lens array. FIG. 7A is a plan view of the lens array 301 viewed from above, and FIG. 7B is a cross-sectional view taken on line VIIBxe2x80x94VIIB in FIG. 7A, viewed from the arrow direction. A region corresponding to one pixel (hereinafter occasionally referred to as a xe2x80x9cpixel regionxe2x80x9d) is a region defined by vertical sides 355 and horizontal sides 354. The lens 301 is provided substantially at the center of the foregoing region to contribute to the improvement in sensitivity. Here, spaces 353 are provided between adjacent lenses from the viewpoint of manufacture. Incidentally, though only four pixels are shown in FIGS. 7A and 7B for simplification of the drawings, predetermined numbers of pixels shown in FIG. 7A actually are aligned in the vertical and horizontal directions, respectively.
In the foregoing lens array, each lens is substantially round or elliptic in planar shape and has a diameter not exceeding a length of one side of the pixel-corresponding region. Therefore, the spaces 353 produced in the manufacturing process are present in each of the lens-alignment directions. Further, in each tetragonal pixel region, there also are spaces at corners where the lens 301 is not formed. Light incident on these portions hardly enters the light receiving sections, hence making substantially no contribution to the sensitivity.
Likewise, a lens array having spaces as shown in FIGS. 7A and 7B is laminated in a fashion such that each lens should correspond to each pixel, in a panel display element used in a transparent-type liquid crystal display as well. However, light entering the foregoing spaces does not contribute to the luminance of a screen of the liquid crystal display.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a lens array arranged, for example, so as to include lenses each having a greater aperture and a sufficient curvature for collecting light, so that the lens array, for instance, can achieve improvements in sensitivity when used in a solid-state imaging element, and improvements in luminance of a screen when used in a panel display element.
In order to achieve the aforementioned object, a lens array of the present invention has the following configuration.
Namely, a lens array according to a first configuration of the present invention includes a plurality of condenser lenses arrayed in vertical and horizontal directions so that the condenser lenses and pixels arrayed in a two-dimensional plane have one-to-one correspondence. The lens array is characterized in that each of the condenser lenses, when viewed from a direction perpendicular to a condenser lens-arrayed plane, has a planar shape formed with four straight sides and four approximate circular arcs extending between the respective straight sides, and the center of the four approximate circular arcs substantially coincides with the center of a region corresponding to the pixel.
The lens array according to the first configuration ensures efficient utilization of each pixel region, thereby increasing the aperture of the condenser lens and reducing the loss of light passing through the pixel regions. This results in, for instance, improvement of sensitivity when the lens array is used in a solid-state imaging element, and improvement of luminance of a screen when the lens array is used in a panel display element. In addition, it is relatively easy to manufacture lenses in the aforementioned shape.
In the first configuration, it is preferable that the pixel-corresponding region be rectangular (either rectangular or square) in shape, and that a diameter of the approximate circular arcs be shorter than a diagonal of the region while being longer than a short side of the region (a vertical or horizontal side of the region in case it is square). The foregoing preferable configuration allows a proportion of a condenser-lens-provided area in the pixel region to increase, thereby causing the condenser lens to have a larger aperture.
Furthermore, in the first configuration, it is preferable that the pixel-corresponding region be rectangular (either rectangular or square) in shape, and that the condenser lens has a substantially equal curvature in diagonal and side directions in the region. The foregoing preferable configuration allows a lens array having a multiplicity of condenser lenses arrayed in the vertical and horizontal directions to be formed through a simple process described later.
Furthermore, in the first configuration, it is preferable that the pixel-corresponding region be rectangular (either rectangular or square) in shape, and that a radius of curvature R of the condenser lens satisfies:
X/2xe2x89xa6Rxe2x89xa6(xc2xd)xc3x97(X2+Y2)xc2xdxe2x80x83xe2x80x83(1)
where X and Y represent a length of a short side and a length of a long side of the region, respectively (X=Y when the foregoing region is square), in either a vertical or horizontal direction in the region.
The foregoing preferable configuration allows a proportion of a condenser-lens-provided area in the pixel region to increase, thereby causing the condenser lens to have a larger aperture.
A lens array according to a second configuration of the present invention includes a plurality of condenser lenses arrayed in vertical and horizontal directions so that the condenser lenses and pixels arrayed in a two-dimensional plane have one-to-one correspondence. The lens array is characterized in that each of regions corresponding to the pixels, respectively, is rectangular in shape, and a short side of the region is not longer than xc2xd of a long side of the same, that each of the condenser lenses, when viewed from a direction perpendicular to a condenser lens-arrayed plane, has a planar shape formed with two straight sides opposing each other substantially in parallel and two approximate circular arcs extending between the straight sides, and further, that a center of the two approximate circular arcs substantially coincides with a center of the pixel-corresponding region.
The foregoing lens array according to the second configuration ensures efficient utilization of each pixel region in the case where the array pitch of the pixels in the vertical direction differs from that in the horizontal direction, thereby increasing an aperture of the condenser lens and reducing the loss of light passing through the pixel regions. This results in, for instance, improvement in sensitivity when the lens array is used in a solid-state imaging element, and improvement in luminance of a screen when the lens array is used in a panel display element. In addition, it is relatively easy to manufacture lenses in the aforementioned shape.
In the first or second configuration, it is preferable that side surfaces of the condenser lens that respectively include the straight sides of the planar shape of the condenser lens not be perpendicular to the condenser lens-arrayed plane. With the foregoing preferable configuration, when used in a solid-state imaging element, it also is possible to guide light entering the side surfaces efficiently to the light receiving sections. Furthermore, when an angle of tilt of the side surfaces is selected with a manufacturing method taken into consideration, an easily manufacturable lens array can be obtained.
In the first or second configuration, it is preferable that the pixel-corresponding region be rectangular (either rectangular or square) in shape, and that a short side of the rectangular region (one side of the region when it is square) be not more than 5 xcexcm long, and more preferably not more than 3.5 xcexcm long. The foregoing preferable configuration facilitates manufacture of the condenser lens whose radii of curvature in the diagonal and side directions of the foregoing region are substantially equal to each other.
Furthermore, in the first or second configuration, the condenser lens preferably is not more than 2 xcexcm high, and more preferably not more than 1 xcexcm high. The foregoing preferable configuration facilitates manufacture of the condenser lens whose radii of curvature in the diagonal and side directions of the foregoing region are substantially equal to each other.
Furthermore, in the first or second configuration, the condenser lens preferably is formed in a binary shape obtained by approximation of its shape to a step-like shape. The foregoing preferable configuration allows more alternatives of lens array manufacturing methods to be available, thereby enabling simplification of a manufacturing process and cost reduction.
Furthermore, a solid-state imaging element according to the present invention includes light receiving sections arrayed in a two-dimensional plane and the lens array according to the first or second configuration that is laminated on the light receiving sections. The solid-state imaging element is characterized in that the condenser lenses of the lens array and the light receiving sections have one-to-one correspondence. The foregoing configuration ensures that a solid-state imaging element having high sensitivity and being capable of providing sharp images can be provided. In the present invention, the xe2x80x9csolid-state imaging elementxe2x80x9d means a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS).
In the foregoing configuration, a focal length of the condenser lens preferably is substantially equal to a distance therefrom to the light receiving section corresponding thereto. The foregoing preferable configuration ensures that light passing through the condenser lens can be gathered and directed to the light receiving section without loss, thereby increasing a virtual aperture of the condenser lens. Consequently, sharp images can be obtained.
Furthermore, a panel display element in accordance with the present invention includes pixels arrayed in a two-dimensional plane and the lens array according to the first or second configuration that is laminated on the pixels. The panel display element is characterized in that the condenser lenses of the lens array and the pixels have one-to-one correspondence. According to the foregoing configuration, it is possible to obtain a panel display element having improved luminance of a screen and being capable of providing sharp images. In the present invention, the xe2x80x9cpanel display elementxe2x80x9d means a liquid crystal display element or an organic electro-luminescence (EL) device.
In the foregoing configuration, a focal length of the condenser lens preferably is substantially equal to a distance therefrom to the pixel corresponding thereto. The foregoing preferable configuration increases a virtual aperture of the condenser lens. Consequently, sharp images can be obtained.